US 7324433 B1 Abstract The present invention is directed to a method, program product, and apparatus that determines a signal quality associated with a symbol modulated signal based on a scalar relationship based on at least one of a comparison of plural correlation candidates for a symbol in the modulated signal or a comparison of the vector corresponding to a decided symbol against a reference. In accordance with one aspect of the present invention, a method and apparatus are disclosed which involve determining maximum and next-maximum correlation candidates for a symbol perceived in the modulated signal, calculating the scalar relationship between the maximum and next-maximum correlation candidates, and deriving a signal quality associated with the modulated signal based on the scalar relationship. In accordance with another aspect of the present invention, a method and apparatus are disclosed which involve determining a decided symbol for the symbol perceived in the modulated signal, calculating a scalar relationship between a vector corresponding to the decided symbol and a reference, and deriving a signal quality associated with the modulated signal based on the scalar relationship. In accordance with either of these aspects, the derived signal quality can be used to alter one or more receiver characteristics of a receiver used to capture the modulated signal.
Claims(72) 1. A method comprising:
determining maximum and next-maximum correlation candidates for a symbol perceived within a modulated signal;
calculating a scalar relationship between the maximum and next-maximum correlation candidates;
deriving a signal quality associated with the modulated signal based on the scalar relationship; and
altering a receiver characteristic based on said derived signal quality.
2. The method of
the symbol is defined by a plurality of chips; and
wherein said determining step comprises:
correlating the chips of the symbol against a plurality of possible candidate vectors;
first selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol pursuant to said correlating step; and
second selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol pursuant to said correlating step.
3. The method of
4. The method of
said correlating step includes the step of generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and
wherein said first and second selecting steps comprises assessing the correlation parameters using one of:
a sequential comparison process following the first order; and
a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.
5. The method of
6. The method of
7. The method of
a distance between the maximum and next-maximum correlation candidates; and
a magnitude difference between the maximum and next-maximum correlation candidates.
8. The method of
receiving the modulated signal in accordance with a receiver characteristic; and
modifying the receiver characteristic based on the derived signal quality.
9. A method comprising:
determining a decided symbol for a symbol perceived within a modulated signal;
calculating a scalar relationship between a vector corresponding to the decided symbol and a reference;
deriving a signal quality associated with the modulated signal based on the scalar relationship; and
altering a receiver characteristic based on said derived signal quality.
10. The method of
comparing the scalar relationship to a threshold;
generating a first signal if the scalar relationship is less than the threshold; and
generating a second signal if the scalar relationship at least meets the threshold.
11. The method of
receiving the modulated signal in accordance with a receiver characteristic; and
modifying the receiver characteristic based if the derived signal quality comprises the first signal.
12. The method of
receiving the modulated signal in accordance with a receiver characteristic; and
modifying the receiver characteristic based on the derived signal quality.
13. The method of
14. A computer-readable storage medium that stores a program code that causes an information processor to perform at least the following steps, the steps comprising:
determining maximum and next-maximum correlation candidates for a symbol perceived within a modulated signal;
calculating a scalar relationship between the maximum and next-maximum correlation candidates;
deriving a signal quality associated with the modulated signal based on the scalar relationship; and
altering a receiver characteristic based on said derived signal quality.
15. The computer-readable storage medium of
the symbol is defined by a plurality of chips; and
wherein said determining step comprises:
correlating the chips of the symbol against a plurality of possible candidate vectors;
first selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol pursuant to said correlating step; and
second selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol pursuant to said correlating step.
16. The computer-readable storage medium of
17. The computer-readable storage medium of
said correlating step includes the step of generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and
wherein said first and second selecting steps comprises assessing the correlation parameters using one of:
a sequential comparison process following the first order; and
a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.
18. The computer-readable storage medium of
19. The computer-readable storage medium of
20. The computer-readable storage medium of
a distance between the maximum and next-maximum correlation candidates; and
a magnitude difference between the maximum and next-maximum correlation candidates.
21. The computer-readable storage medium of
receiving the modulated signal in accordance with a receiver characteristic; and
modifying the receiver characteristic based on the derived signal quality.
22. A computer-readable storage medium that stores program code that causes an information processor to perform at least the following steps, the steps comprising:
determining a decided symbol for a symbol perceived within the modulated signal;
calculating a scalar relationship between a vector corresponding to the decided symbol and a reference;
deriving a signal quality associated with the modulated signal based on the scalar relationship; and
altering a receiver characteristic based on said derived signal quality.
23. The computer-readable storage medium of
generating a first signal if the scalar relationship is less than the threshold; and
generating a second signal if the scalar relationship at least meets the threshold.
24. The computer-readable storage medium of
receiving the modulated signal in accordance with a receiver characteristic; and
modifying the receiver characteristic based if the derived signal quality comprises the first signal.
25. The computer-readable storage medium of
receiving the modulated signal in accordance with a receiver characteristic; and
modifying the receiver characteristic based if the derived signal quality comprises the first signal.
26. The computer-readable storage medium of
27. A symbol processor operable upon a symbol modulated signal, the symbol processor comprising:
a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;
a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates;
a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and
at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.
28. The symbol processor of
the symbol is defined by a plurality of chips; and
wherein said candidate determination unit comprises:
a correlator to correlate the chips of the symbol against a plurality of possible candidate vectors; and
a comparator coupled to said correlator, the comparator capable of selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.
29. The symbol processor of
30. The symbol processor of
said correlator includes a vector analysis unit coupled to said candidate selection logic to generate a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and
wherein said comparator comprises selection logic to assess the correlation parameters using one of:
a sequential comparison process following the first order; and
a modified sequential comparison process following a second order associated with the set of symbol vectors, the second order being dissimilar from the first order.
31. The symbol processor of
32. The symbol processor of
33. The symbol processor of
a distance between the maximum and next-maximum correlation candidates; and
a magnitude difference between the maximum and next-maximum correlation candidates.
34. The symbol processor of
a decided symbol determination unit coupled to said scalar calculation unit to determine a decided symbol for the symbol perceived within the modulated signal; and
wherein said scalar calculation unit calculate a second scalar relationship between a vector corresponding to the decided symbol and a reference; and
wherein said signal quality derivation unit derives a second signal quality associated with the modulated signal based on the second scalar relationship.
35. The symbol processor of
36. A receiver, comprising:
a receive unit to receive a modulated signal in accordance with a receiver characteristic;
a symbol processor coupled to the receive unit, comprising:
a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;
a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and
a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and
at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.
37. The receiver of
38. The receiver of
the symbol is defined by a plurality of chips; and
wherein said candidate determination unit comprises:
a correlator to correlate the chips of the symbol against a plurality of possible candidate vectors; and
a comparator coupled to said correlator, the comparator capable of selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.
39. The receiver of
40. The receiver of
said correlator includes a vector analysis unit coupled to said candidate selection logic to generate a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and
wherein said comparator comprises selection logic to assess the correlation parameters using one of:
a sequential comparison process following the first order; and
41. The receiver of
42. The receiver of
43. The receiver of
a distance between the maximum and next-maximum correlation candidates; and
a magnitude difference between the maximum and next-maximum correlation candidates.
44. The receiver of
a decided symbol determination unit coupled to said scalar calculation unit to determine a decided symbol for the symbol perceived within the modulated signal; and
wherein said scalar calculation unit calculates a second scalar relationship between a vector corresponding to the decided symbol and a reference; and
wherein said signal quality derivation unit derives a second signal quality associated with the modulated signal based on the second scalar relationship.
45. The receiver of
46. A transceiver, comprising:
a transmitter;
a receiver to receive a modulate signal in accordance with a receiver characteristic;
a symbol processor coupled to said receiver and said transmitter, said symbol processor comprising:
a candidate determination unit to determine maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;
a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and
a signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and
at least one of a radio frequency (RF) unit and a media access controller (MAC) interface to alter a receiver characteristic based on said derived signal quality.
47. A base station, comprising:
an antenna;
a transmitter and a receiver coupled to said antenna, said receiver comprising:
a receive unit to receive a modulated signal in accordance with a receiver characteristic;
a symbol processor coupled to said receive unit, said symbol processor comprising:
a scalar calculation unit coupled to said candidate determination unit to calculate a scalar relationship between the maximum and next-maximum correlation candidates; and
48. A network interface, comprising:
a data interface;
a receiver coupled to said data interface, said receiver comprising:
a receive unit to receive a modulated signal in accordance with a receiver characteristic; and
a symbol processor coupled to said receive unit, said symbol processor comprising:
49. An information processing system, comprising:
an information processor coupled to a data interface;
a receiver coupled to said data interface, said receiver comprising
a receive unit to receive a modulated signal in accordance with a receiver characteristic; and
a symbol processor coupled to said receive unit, said symbol processor comprising:
signal quality derivation unit coupled to said scalar calculation unit to derive a signal quality associated with the modulated signal based on the scalar relationship; and
50. A symbol processor operable upon a symbol modulated signal, the symbol processor comprising:
means for determining maximum and next-maximum correlation candidates for a symbol perceived within the modulated signal;
means for calculation a scalar relationship between the maximum and next-maximum correlation candidates;
means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and
means for altering a receiver characteristic based on said derived signal quality.
51. The symbol processor of
the symbol is defined by a plurality of chips; and
wherein said determining means comprises:
means for correlating the chips of the symbol against a plurality of possible candidate vectors; and
means for selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.
52. The symbol processor of
53. The symbol processor of
said correlating means includes means for generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and
wherein said selecting means includes means for assessing the correlation parameters using one of:
a sequential comparison process following the first order; and
54. The symbol processor of
55. The symbol processor of
56. The symbol processor of
a distance between the maximum and next-maximum correlation candidates; and
a magnitude difference between the maximum and next-maximum correlation candidates.
57. The symbol processor of
means for determining a decided symbol for the symbol perceived within the modulated signal;
means for calculating a second scalar relationship between a vector corresponding to the decided symbol and a reference; and
means for deriving a second signal quality associated with the modulated signal based on the second scalar relationship.
58. The symbol processor of
means for comparing the scalar relationship to a threshold; and
means for generating one of a first signal if the second scalar relationship is less than the threshold and a second signal if the second scalar relationship at least meets the threshold.
59. A receiver, comprising:
means for receiving a modulated signal in accordance with a receiver characteristic;
means for processing a symbol perceived within the modulated symbol, comprising:
means for determining maximum and next-maximum correlation candidates for the symbol;
means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and
means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and
means for altering a receiver characteristic based on said derived signal quality.
60. The receiver of
61. The receiver of
the symbol is defined by a plurality of chips; and
wherein said determining means comprises:
means for correlating the chips of the symbol against a plurality of possible candidate vectors; and
means for selecting as the maximum correlation candidate one of the plurality of possible candidate vectors most correlated to the chips of the symbol and capable of selecting as the next-maximum correlation candidate at least one of the plurality of possible candidate vectors other than the maximum correlation candidate most relatively correlated to the chips of the symbol.
62. The receiver of
63. The receiver of
said correlating means includes means for generating a correlation parameter for each of the plurality of possible candidate vectors with respect to the chips of the symbol; and
wherein said selecting means comprises means for assessing the correlation parameters using one of:
a sequential comparison process following the first order; and
64. The receiver of
65. The receiver of
66. The receiver of
a distance between the maximum and next-maximum correlation candidates; and
a magnitude difference between the maximum and next-maximum correlative candidates.
67. The receiver of
means for determining a decided symbol for the symbol perceived within the modulated signal;
means for calculating a second scalar relationship between a vector corresponding to the decided symbol and a reference; and
means for deriving a second signal quality associated with the modulated signal based on the second scalar relationship.
68. The receiver of
69. A transceiver, comprising:
means for transmitting a first modulated signal;
means for receiving a second modulated signal in accordance with a receiver characteristic;
means for processing a symbol perceived within the modulated symbol, comprising:
means for determining maximum and next-maximum correlation candidates for the symbol;
means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and
means for deriving a signal quality associated with the modulated signal based on the scalar relationship; and
means for altering a receiver characteristic based on said derived signal quality.
70. A base station, comprising:
means for transmitting and receiving a modulated signal, said receiving means comprising:
means for receiving the modulated signal in accordance with a receiver characteristic;
means for processing a symbol perceived within the modulated symbol, comprising:
means for determining maximum and next-maximum correlation candidates for the symbol;
means for calculating a scalar relationship between the maximum and next-maximum correlation candidates; and
means for altering a receiver characteristic based on said derived signal quality.
71. A network interface, comprising:
means for transferring data;
means for receiving a modulated signal, comprising:
means for receiving the modulated signal in accordance with a receiver characteristic; and
means for determining maximum and next-maximum correlation candidates for the symbol;
means for altering a receiver characteristic based on said derived signal quality.
72. An information processing system, comprising:
means for processing information;
means for receiving a modulated signal responsive to said information processing means, said receiving means comprising:
means for receiving the modulated signal in accordance with a receiver characteristic; and
means for determining maximum and next-maximum correlation candidates for the symbol;
means for altering a receiver characteristic based on said derived signal quality.
Description This application claims priority benefit under 35 U.S.C. § 119(e)(1) to U.S. Provisional Application No. 60/334,347, filed Nov. 29, 2001, entitled Method and Apparatus For Determining Signal Quality, which is incorporated herein fully by reference. This invention is generally concerned with modulated signal receiver performance, and is particularly concerned with techniques for assessing perceived signal quality of a modulated signal derived from processing one or more coded symbols contained within the signal. The past few years has witnessed the ever-increasing availability of relatively cheap, low power wireless data communication services, networks and devices, promising near wire speed transmission and reliability. One technology in particular, described in the IEEE Standard 802.11b-1999 Supplement to the ANSI/IEEE Standard 802.11, 1999 edition, collectively incorporated herein fully by reference, and more commonly referred to as “802.11b” or “WiFi”, has become the darling of the information technology industry and computer enthusiasts alike as a wired LAN/WAN alternative because of its potential 11 Mbps effective data transmission rate, ease of installation and use, and transceiver component costs make it a real and convenient alternative to wired 10 BaseT Ethernet and other cabled data networking alternatives. With 802.11b, workgroup-sized networks can now be deployed in a building in minutes, a campus in days instead of weeks since the demanding task of pulling cable and wiring existing structures is eliminated. Moreover, 802.11b compliant wireless networking equipment is backwards compatible with the earlier 802.11 1 M/2 Mbps standard, thereby further reducing deployment costs in legacy wireless systems. 802.11b achieves relatively high payload data transmission rates through the use of orthogonal class modulation in general, and, more particularly, 8-chip complementary code keying (“CCK”) as a 11 MHz chipping rate. As such, bitstream data is mapped into nearly orthogonal sequences (or code symbols) to be transmitted, where each chip of the code symbol is quaternary phase modulated. An 801.11b compliant receiver correlates the received CCK modulated signal with 64 candidate waveforms to find the most likely code symbol, from which the bitstream data is recovered through reverse mapping. The high-rate physical layer PLCP preamble and header portions are still modulated using the 801.11 compliant Barker spreading sequence at an 11 MHz chipping rate, resulting in a 1 or 2 Mbps effective header and preamble transmission rate depending on whether DBPSK or DQPSK modulation is employed. CCK was chosen in part because of its strong inherent resistance to multipath interference, which is likely to be encountered in the typical in-building deployment. Nevertheless, the confluence of strict power/noise limits specified for operation in the 2.4 GHz ISM band and megabit+expected data throughput rates limits conventional 802.11b to just a 100 or so feet between stations, depending on the number of interposing radio obstructions and reflections. Thus 802.11b remains susceptible to multipath interference, and to reception errors produced by inter-symbol (“ISI”) and inter-chip interference(“ICI”) in particular. To combat this, designers have sought to improve receiver performance, at least with respect to CCK code symbol demodulation by using active equalization techniques. However, such techniques do not appear to take into account symbol processing reliability or errors, much less track such errors, nor alter the transmission environment when post symbol processing signal quality degrades. To address these and other perceived shortcomings, the present invention is directed to a method, program product, and apparatus that determines a signal quality associated with a symbol modulated signal based on a scalar relationship based on at least one of a comparison of plural correlation candidate for a symbol in the modulated signal or a comparison of the vector corresponding to a decided symbol against a reference. In accordance with one aspect of the present invention, a method and apparatus are disclosed which involve determining maximum and next-maximum correlation candidates for a symbol perceived in the modulated signal, calculating the scalar relationship between the maximum and next-maximum correlation candidates, and deriving a signal quality associated with the modulated signal based on the scalar relationship. In accordance with another aspect of the present invention, a method and apparatus are disclosed which involve determining a decided symbol for the symbol perceived in the modulated signal, calculating a scalar relationship between a vector corresponding to the decided symbol and a reference, and deriving a signal quality associated with the modulated signal based on the scalar relationship. In accordance with either of these aspects, the derived signal quality can be used to alter one or more receiver characteristics of a receiver used to capture the modulated signal. Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof, which proceeds with reference to the accompanying drawings. Turning first to The ADC It should be noted here that the digital baseband signal The transmit pathway includes the scrambler The receive pathway, namely the receiver components of RF unit Also, in this embodiment, the receive symbol processor In the embodiment shown in A more detailed discussion of the relevant functions and composition of the receive symbol processor Turning first to the determination units Considering first the situation where Barker demodulation is needed, the Barker correlator The comparison unit Considering now where the current symbol is CCK-encoded (i.e. mod_type=CCK), the CCK denudation pathway of the candidate determination unit Once all chips defining the current CCK modulated symbol have been equalized and accumulated by the latch Consistent with the present embodiment, several techniques may be used to single out the possible candidate vectors, including parallel correction against the entire set of CCK symbol vectors followed by selective comparison of correlation results involving only the possible candidate vectors, flagging the possible candidates presented in a larger table accommodating the entire set of CCK symbol vectors and correcting only these candidates against the latched symbol chips, etc. Herein, the set of CCK symbol vectors may be conveniently set forth in a lookup table such as vector table (“VT”) Though not required, the CCK correlator More detail on correlation processing may be found in e.g. U.S. patent application Ser. No. 10/092,971, filed Mar. 5, 2002naming Guorong Hu, Yungping Hsu, and Weishi Feng as co-inventors and entitled METHOD AND APPARATUS FOR COMPLEMENTARY CODE KEYING, which is incorporated herein fully by reference. As discussed above, signal quality consistent with the present embodiment may be realized through comparative vector analysis of the maximum correlation candidate and the next-maximum correlation candidate(s), defined herein as one or more possible candidate vectors having the relatively next-highest correction parameter value(labeled “MAX To better understand the relationship between the maximum correlation candidate and the next-maximum correlation candidate, consider a sample plot of correlation parameter produced by a CCK correlator In the embodiment of It should be noted that the components of the receive symbol processor Although not shown in the figures, consistent with the present embodiment the MAC+layers serviced by the transceiver Moreover, although the present embodiment contemplates certain types of scalar relationships (e.g. Barker mode—magnitude of the real and imaginary components of the decided symbol vector which is essentially a scalar difference between the decided symbol vector and nil, or CCK mode—difference in correlation parameters for the maximum and next-maximum correlation candidates), other types of scalar relationships may be used consistent with the present invention in order to derive an appropriate measure of signal quality based on perceived processing gain reliability and/or errors. For example, in CCK mode, a scalar or Euclidean distance between maximum and next-maximum correlation candidate vectors may be calculated and thresholded to determine if there's signal quality problem (again a higher number indicates a more reliable correlation decision has been reached. Turning now to However, by exploiting relative distance relationships within subsets of CCK vectors, one can group together and re-order comparions according to a second order (depicted as order Consider first the set of possible candidate vectors defined where φ3=0. In this case, group of vectors The local maximum for the remaining vector groups According to this embodiment, the modified sequential comparison process continues until the maximum max It will be obvious to those having ordinary skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. For example, though the above-described embodiments are directed to implementations compliant with IEEE 802.11 and 802.11b standard, the teachings of the present invention are not intended to be so limiting and in fact post symbol processing signal quality consistent with the present invention can be derived in other coded symbol reception scenarios and environments, whether based on RF transmission or otherwise. The scope of the present invention should, therefore, be determined only by the following claims. Patent Citations
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